1. Field of the Art
This invention relates to a method for dynamic control of the end-point of the converter blow.
2. Description of the Prior Art
In converter processes, control for increasing the predictability of carbon content and bath temperature in the final stage of blow to thereby obtain slags with improved chemical compositions plays an important role and has so far been the subject of much study. For example, it has been proposed to estimate the carbon content of the bath solely based on the rate of carburization near the end-point of the blow and, thereby, control the end-point carbon content. This procedure, however, is not only liable to significant errors due, for example, to changes in amount of the slag formed on the bath surface, and the consequent large variation of accuracy, but also has the disadvantage that it cannot be used for temperature control or to detect the iron oxide content of the slag. Recently the sublance method has been widely and successfully utilized wherein the carbon content and temperature of the bath are directly measured by means of sublances for end-point control purposes. However, this method is not only disadvantageous in that measuring errors due to the uneven distribution of chemical components and temperature in the bath must be solved with some ingenuity but has the drawback that the iron oxide content of the slag cannot be determined. There has also been reported a control system wherein waste gas information is constantly read and updated and the parameters of a decarburization rate model expression are determined using the up-to-date information. Notwithstanding the complicated computations required, it is said that the method is inadequate in predictability. Moreover, the following specific procedures have recently been proposed for blow control based on a combination of carbon content measured by sublance (C.sub.SL) with waste gas information. A first of these procedures is one using C.sub.SL as an integral constant ("Tetsu-to-Hagane" 62, 4, p. 114). ##EQU2## Where C.sub.E : The carbon content of the bath at endpoint of the blow
C.sub.SL : The carbon content of the bath at the time-point of sublance measurement PA1 t.sub.E : time of blow end point PA1 t.sub.SL : the time of sublance measurement PA1 K: A coefficient for conversion of the amount (kg) of carbon to the concentration (%) of carbon
However, as will be readily understood from the above equation, this control method using an integral value of decarburization rate is not practically useful, because .sigma.(C.sub.E).gtoreq..delta.(C.sub.SL) and, hence, the error in the sublance measurement is controlling over the accuracy of carbon content at the end point of the blow [the uneven distribution of chemical constituents in the bath and the error inherent in the rapid carbon analysis (Carbon content detector), taken together, result in a fairly large error in measured C.sub.SL value].
A second control method, which is reported in Tetsu-to-Hagane 63, 9, p. 21, is such that control is carried out by means of an arbitrary parameter in the equation for obtaining dc/dt from C.sub.SL ' and .phi..sub.SL (Oxygen efficiency for decarburization at the time of sublance measurement) (In the reported case, as to the equation dc/dt=.alpha.+.beta. exp(-.gamma.c), .beta. is determined from C.sub.SL and .phi..sub.SL). However, because this method disregards .tau.. Carbon content in the bath is estimated only inaccurately. Moreover, when use is made of a parameter such as that used in the reported case, the indefinite physical meaning of the parameter fails to provide a clear picture of its relationship with other factors in converter blow [T control (control of the bath temperature at the end point of the blow) and detection of the iron oxide content of the slag] which is possible in the case of this invention. Thus, attempts to correlate the sublance information with the waste gas information have so far failed to meet with success.